The present invention relates to a method for producing crystalline alkali metal silicate granules. More specifically, the present invention relates to a method for producing crystalline alkali metal silicate granules, which can be stably formulated in other detergents without deteriorating the properties of the crystalline alkali metal silicate, and further have extremely high detergent activity. Also, the present invention relates to a granular detergent composition having a high bulk density and a washing method. More specifically, the present invention relates to a granular detergent composition having a high bulk density which has excellent powder properties and is capable of having excellent detergency with a small standard amount of dosage thereof, and a washing method using the above granular detergent composition.
A method of granulating crystalline silicates, such as crystalline alkali metal silicates, is disclosed in Japanese Patent Laid-Open No. 3-164422. Here, the method for preparing granules having a high bulk density of from 700 to 1000 g/liter comprises powdering crystalline sodium silicate to a size of from 2 to 400 xcexcm using a mechanical disintegrator, pressing the powdered silicate with a roller compactor (20 to 40 kN/1 cm width) to give dense materials, comminuting by forcing the silicates through screens, and sieving the comminuted materials. However, it would be impossible to prevent the deterioration of the performance owing to its hygroscopic property, which is an inherent property of the crystalline alkali metal silicates, or to suppress the caking phenomenon caused by consolidation of the crystalline alkali metal silicate owing to their hygroscopic properties. Also, the breaking of the granules during conveying is likely to take place.
Japanese Patent Unexamined Publication No. 6-502445 discloses a method for producing a free-flowable aggregate by blending in an energy-intensive mixer an aluminosilicate or a layered silicate with a particular binder. However, the binder which contains water is undesirable for maintaining excellent performance of the crystalline silicates. Also, the aqueous polymer is needed to be added in an amount of 10 parts or more, but this ingredient gives substantially no contribution to the detergency performance, thereby making it disadvantageous for the purpose of concentrating the composition.
Also, Japanese Patent Laid-Open No. 5-209200 discloses a method for producing a nonionic surfactant-containing granulated product, comprising the steps of agitating and blending a mixture of detergent starting materials containing a nonionic surfactant as a main surfactant component in an agitating mixer, the agitating mixer containing an agitating shaft along the center line of the inner portion, agitation impellers arranged along the agitating shaft, and a clearance formed upon rotating the agitating impellers between the agitating impellers and a wall of the agitating mixer, to thereby form a layer of the detergent starting materials adhered to the wall of the agitating mixer; and granulating the obtained mixture while increasing the bulk density of the detergent starting materials by the agitating impellers. However, since the nonionic surfactant is supported by the capillary force or the surface adsorption of the powdery starting materials, the supporting force is weak. Therefore, although the resulting granulated product has no problems at a practical level, sufficient adhesion of the nonionic surfactant-containing powder to the equipment upon conveying or sufficient exudation inhibition cannot be achieved, as compared to that of the present invention when packing the powder in a carton package.
Moreover, to date, various kinds of chelating agents, ion exchange materials, alkalizers, and dispersants have been known to be used for builders to be blended in detergents. Particularly, the phosphorus-based chelating agents such as tripolyphosphates as a main component thereof have good water solubility and detergency, so that they have been formulated as main detergent builder components.
In recent years, however, the use of tripolyphosphates has decreased, since they can cause eutrophication in closed freshwater areas such as lakes and marshes. Instead, crystalline aluminosilicates (zeolites) have been commonly used as substitutes for the metal ion capturing agent. Many patent applications have been filed concerning the formulation of crystalline aluminosilicates in detergents, as typically disclosed in Japanese Patent Laid-Open No. 50-12381. In addition, Yushi (Vol, 32, No.1, pp.36-40 (January 1979)) discloses the substitution to zeolites which took place at that time.
The rapid progress has taken place in changes in use of phosphorus-free detergents by substituting with zeolites, but the formulation of zeolites is merely a substitution of phosphorus-containing builders, which are used to produce detergents with a low bulk density of 0.2 to 0.4 g/cm3. Such detergents would require a standard amount of dosage of 40 g and 100 to 200 cm3 per one washing cycle, the washing cycle being most commonly using about 30 L of the washing liquid per one cycle in Japan. Therefore, in the case where detergents for about 60 to about 100 washing cycles are placed in a carton package, the resulting detergent package becomes undesirably heavy as from 2.5 to 4.5 kg and undesirably bulky as from 6000 to 20000 ml. Therefore, much inconveniences were caused in burdening the conveying costs in the plant and carrying inconveniences and storage space for the consumers.
Therefore, an intense investigation has been made to produce compact detergents. For instance, Japanese Patent Laid-Open Nos. 62-167396, 62-167399, and 62-253699 disclose a remarkable decrease in the amount of crystalline inorganic salts such as sodium sulfate used as powdering aids conventionally contained in detergents. In addition, Japanese Patent Laid-Open Nos. 61-69897, 61-69899, 61-69900, and 5-209200 disclose that an increase in the bulk density of the detergents leads to a production of detergents having a bulk density of from 0.60 to 1.00 g/ml, whose standard amount of dosage is from 25 to 30 g/30 L, thereby resulting in making the detergents compact to a level of a standard volumetric amount of dosage of from 25 to 50 ml/30 L.
However, in conventional detergents, a large amount of surfactants had to be blended in the detergent compositions because mainstream of the technical idea was to make the oily components in dirt soluble by surfactants. Specifically, sebum dirt stains ascribed to human bodies, the most typical dirt stains adhered to clothes (most likely to be observed on collars and sleeves), are taken as examples. The sebum dirt stains contains oily components, such as free fatty acids and glycerides, with a high content of 70% or more (Ichiro KASHIWA et al., xe2x80x9cYukagaku,xe2x80x9d 19, 1095 (1969)). The oily components lock carbon and dirt in dust and peeled keratin, so that the resulting substance is observed as dirt stains. In order to wash off the sebum dirt stains, conventional detergents are designed based on a washing mechanism mainly by making these oily components soluble with micelle of surfactants, thereby detaching carbon, dirt, and keratin from clothes. This technical idea has been widely established among those of ordinary skill in the art, and even when the conventional detergents are shifted to compact detergents, substantially no changes took place in the surfactant concentration in the washing liquid. This fact is described in xe2x80x9cDictionary for Detergents and Washing,xe2x80x9d Haruhiko OKUYAMA et al., p. 428, 1990, First Edition, Asakura Publishing Company Limited, which shows that there are substantially no changes in concentrations in the washing liquid for components other than sodium sulfate.
Based on these washing principles, the surfactant concentration in the washing liquid has to be made high in order to achieve high washing power, so that a large amount of surfactants has to be blended in the detergent composition. Therefore, a drastic reduction in the standard amount of dosage of the detergents was actually difficult. In addition, the presently known production method substantially enables to increase the bulk density to a level of about at most 1.00 g/ml. Therefore, a further reduction in the standard volumetric amount was deemed to be a technically extremely difficult problem.
On the other hand, crystalline alkali metal silicates having particular structure disclosed in Japanese Patent Laid-Open Nos. 5-184946 and 60-227895 shows not only good ion exchange capacity and alkalizing action (alkalizing ability). Therefore, possibility of more compact detergents has been studied because both of the functions which conventionally was satisfied by two different components, such as metal ion capturing agents, such as zeolites, and alkalizers, such as sodium carbonate, can be satisfied with the above crystalline alkali metal silicates alone.
For instance, Japanese Patent Laid-Open No. 6-116588 is concerned with a detergent composition containing a crystalline silicate. In Examples of this publication disclosing a more compact detergent, even in a case where the amount of the detergent composition at washing is reduced by 25%, the detergent composition has a washing power substantially the same as conventional detergent compositions. However, since the composition is formulated based on the conventional washing principle, the surfactant concentration is high, and the alkalizing ability and the ion exchange capacity are ascribed solely to the crystalline silicates contained therein. In this case, the functions of the crystalline silicates as alkalis precede their functions as metal ion capturing agents, so that the washing power of the detergent composition is not always satisfactory. Therefore, if the amount of dosage of the detergent composition were reduced, a good washing power is not able to be maintained.
A number of patent applications have been filed concerning the crystalline silicates disclosed in Japanese Patent Laid-Open No. 60-227895. Japanese Patent Unexamined Publication No. 6-502199 discloses a detergent comprising a layered crystalline silicate, a zeolite, and a polycarboxylate in particular proportions, to thereby provide a detergent which is free from providing film layer formation on fibers and has excellent washing power and bleaching agent stability. However, under the blending conditions given in this publication, when the amount of the detergents added was reduced at washing, the alkalizing ability is not sufficient because the amount of silicate in the builder composition is small, thereby making it impossible to maintain good washing power. Also, this publication never teaches the technical idea that an excellent washing power is exhibited with small detergent dosages.
The technical idea that an excellent washing power is exhibited using a small amount of detergents, as in the present invention, cannot be found for detergents containing crystalline silicates disclosed in Japanese Unexamined Patent Publication 6-500141, Japanese Patent Laid-Open Nos 2-178398 and 2-178399. Rather, in the case where the amounts of the detergent compositions shown in each of Examples are reduced, the washing power is lowered.
Accordingly, an object of the present invention is to provide crystalline alkali metal silicate granules having a high bulk density, good powder flowability and non-caking ability and free from exudation property.
Another object of the present invention is to provide a granular detergent composition having the same level or higher detergency with a notably smaller standard amount of dosage, and a washing method using such a granular detergent composition.
These and other objects of the present invention will be apparent from the following description.
As a result of intense research in view of the above objects, the present inventors have found that in a system substantially containing no water, crystalline alkali metal silicate granules having extremely high detergent activity may be produced by blending a crystalline alkali metal silicate with an acid precursor of an anionic surfactant capable of having lamellar orientation and a nonionic surfactant, and neutralizing the acid precursor, thereby forming a gelation product containing a nonionic surfactant; and granulating by tumbling a mixture of detergent starting materials while increasing bulk density in an agitating mixer using the gelation product as a binder. In addition, the present inventors have found that by adding a water-soluble nonionic organic compound having a melting point of 45xc2x0 C. or higher and a weight-average molecular weight of 1000 or higher to obtain a starting material mixture of a detergent in the blending step, the exudation property of the nonionic surfactant even in a long-term storage can be suppressed, and good non-blocking property and non-caking ability can be achieved in the resulting crystalline alkali metal silicate granules.
Further, the present inventors have developed a detergent showing excellent detergency with a small standard amount of dosage and good powder properties by blending a nonionic surfactant, an anionic surfactant capable of having a lamellar orientation, a particular crystalline alkali metal silicate, and a metal ion capturing agent in particular proportions.
Specifically, while studying the washing liquid capable of showing good detergency, the present inventors have found that the higher the pH and the lower the water hardness, the dependency of the detergency on the surfactant concentration is lessened, so that good detergency can be achieved. Also, in the case of a high pH but a high water hardness, the detergency is drastically lowered even at a high pH. In the case of washing solely with a composition containing a surfactant but containing no alkalizers, although the detergency at low water hardness is low, the dependency of the detergency on the water hardness is sufficiently small when compared to systems containing alkalizers. From these results, the present inventors have paid attention to the relationship between the washing liquid and the dirt stains.
As discussed in the Background Art section of the present invention, the sebum dirt stains which are the most typical dirt stains adhered to clothes contain free fatty acids and glycerides, and the dirt stains are presumably a mixture of these organic materials with carbon, dirt, or peeled keratin. In the case of a high pH, while the content of the fatty acids increases by hydrolysis of glycerides, the reaction of the fatty acids with alkali metals to form salts also proceeds. The alkali metal salts of the fatty acids are soaps, so that the freeing speed of the dirt stains in the washing liquid becomes notably faster. However, this reaction is a competitive reaction with calcium ions, magnesium ions, etc. in the hard water. Since the alkali metal salts of fatty acids form a scum by carrying out ion-exchange reaction with calcium and magnesium, the dirt stains are solidified without being freed from the interface of clothes in the case where the water hardness is high. For the reasons given above, in the case where the pH is high and the water hardness is low, the washing liquids show excellent detergency, and in the case where the pH is high and the water hardness is high, the washing liquids show notably lowered detergency. Also, in the case where an alkalizer is not formulated, the dependency of the detergency on the water hardness become comparatively lower than the systems containing alkalizers, owing to the fact that the sebum dirt stains are washed only with washing power ascribed to the surfactants.
From these observations, the present inventors have found that one of the reasons for obtaining a detergency at a level equivalent or higher than that obtainable in the conventional detergents even while having a notably lower surfactant concentration value than the conventional detergents is the fact that the soaps formed by the saponification of the glycerides in the dirt stains under the conditions of a low water hardness and a high pH significantly act to give good detergency. In addition, the detergent composition has an excellent detergency at a level equal to or higher than that of the conventional detergents, even when the standard amount of dosage thereof is small and the surfactant concentration in the washing liquid is low, by formulating a surfactant mixture comprising a nonionic surfactant mainly comprising a polyoxyethylene alkyl ethers, which is a surfactant with a low critical micelle concentration (c. m. c.), and an anionic surfactant; a crystalline alkali metal silicate having a high alkaline buffering ability; and a metal ion capturing agent showing a low water hardness in particular proportions. The present invention has been completed based upon these findings.
In one aspect, the present invention is concerned with a method for producing crystalline alkali metal silicate granules, comprising the following steps:
(1) preparing a mixture comprising:
(a) a crystalline alkali metal silicate containing at least SiO2 and M2O, wherein M stands for an alkali metal atom, and an SiO2/M2O molar ratio is from 1.5 to 2.6, wherein a maximum pH value exceeds 11.0 at 20xc2x0 C. in a 0.1% by weight dispersion of the crystalline alkali metal silicate and wherein the crystalline alkali metal silicate has an ion exchange capacity of 100 CaCO3 mg/g or more;
(b) a nonionic surfactant; and
(c) an acid precursor of an anionic surfactant capable of having a lamellar orientation; and
(2) granulating by tumbling the mixture obtained in step (1) with an agitating mixer while increasing a bulk density at a temperature sufficiently high enough to neutralize said acid precursor, to thereby give crystalline alkali metal silicate granules having a bulk density of from 0.6 to 1.2 g/ml.
In a preferred embodiment, the mixture is prepared by further adding (d) other ingredients in step (1).
In this method, the mixture is prepared in step (1) by adding component (c) to the agitating mixer in any one of the following embodiments:
(i) Embodiment where component (c) is added to the agitating mixer together with component (b);
(ii) Embodiment where component (c) is added to the agitating mixer together with component (a) and component (b); or
(iii)Embodiment where component (c) is added to the agitating mixer after component (b) is added to the agitating mixer.
In another embodiment, the mixture is prepared in step (1) by further adding (e) a water-soluble nonionic organic compound having a weight-average molecular weight of 1000 or more and a melting point of 45xc2x0 C. or higher.
In another aspect, the present invention is concerned with a granular detergent composition for clothes washing having high bulk density, comprising the following components:
(I) surfactant components at least comprising:
A) an polyoxyethylene alkyl ether; and
B) an anionic surfactant capable of having a lamellar orientation,
wherein a total amount of component A and component B is 80% by weight or more of the entire surfactant components, and wherein the weight ratio of component A to component B is A/B=20/1 to 1/1;
(II) C) alkali silicate components comprising crystalline alkali metal silicate having an SiO2/M2O molar ratio of 1.5 to 2.6, wherein M stands for an alkali metal atom; and
(III) D) metal ion capturing agents other than component C having a calcium ion capturing ability of 200 CaCO3 mg/g or more,
wherein component I, component II, and component III are present within one granule, and wherein a total amount of component I, component II, and component III is from 70 to 100% by weight of the entire granular detergent composition, wherein the weight ratio of component II to component I is II/I=9/1 to 9/11, and wherein the weight ratio of component II to component III is II/III=4/1 to 1/15, the granular detergent composition having a bulk density being from 0.6 to 1.2 g/ml.
In a preferred embodiment, granule surfaces are coated with amorphous sodium aluminosilicate.
Also, in another preferred embodiment, the granular detergent composition is obtainable by the method for producing crystalline alkali metal silicate described above.
In still another aspect, the present invention is concerned with a washing method comprising the step of washing clothes using the above granular detergent composition for clothes washing having high bulk density, at a surfactant concentration in a washing liquid of from 0.07 to 0.17 g/L.